In the mobile communication system, the terminal establishes a PDN connection appropriate for the purpose of the packet data to be communicated and establishes bearers in the PDN connection to transmit packets. For example, In order to use the Internet Protocol Multimedia Subsystem (IMS) service for receiving the service provided by an operator, it is necessary to establish a connection to the PDN having the IMS servers. Also, in order to use a certain enterprise network for a service, it is necessary to establish a connection to the PDN having the servers capable of establishing Virtual Private Network (VPN) connection to the enterprise network. In order to establish a connection to a PDN appropriate for the purpose, it is possible to use Access Point Name (APN) as a packet data network identifier.
In the current Evolved Packet System (EPS), the terminal establishes a connection to one PDN as default and has to establish a default bearer in the PDN connection during the Attach procedure for registration with the network.
However, a problem may occur when the default PDN specified in the subscriber information is the PDN which cannot establish connection to the destinations of the general applications running on the terminal. In this case, an extra PDN connection has to be established. A representative example is the subscription for use of Voice over LTE (VoLTE). The default PDN connection corresponds to the IMS APN for use of IMS and the extra PDN connection corresponds to the APN indicated in the subscription information for data communication of the normal applications. If the subscriber uses a terminal having no IMS function, the terminal establishes the default PDN connection to the IMS APN although the subscriber has the subscription information capable of allowing both the IMS and normal data communications. Accordingly, unless the subscriber designates an AP explicitly to establish a PDN connection or unless the APN is not designated explicitly in the profile of the application, the PDN connection is always established with the IMS APN. Since the packet data connection established in this case is capable of allowing processing the normal application data, the normal application data are not routed to the destination successfully but dropped, resulting in failure of data communication.